Identification of the incommensurate structure transition in biphenyl by Raman scattering.

Abstract Raman scattering measurements are performed on crystalline biphenyl at low temperatures. The properties of the vibrational modes focused on the intra- and intermolecular terms are analyzed in detail. Nearly all of the vibration modes exhibit hardening and simultaneously sharpen with decreasing temperature, whereas the modes at around 250 cm−1 and 1280 cm−1 soften their energies as temperature is decreased. Moreover, all the internal modes have anomalous reversals at around 45 K on the frequencies, widths, and intensities, and below 45 K, several new internal modes appear. Results of the analyses indicate that the reemergence of the interring tilt angle of the molecules at 45 K has a significant impact on the vibrational properties of biphenyl. Our work thus paves interesting and essential groundwork for the further study of biphenyl. Graphical Abstract Highlights • High resolution Raman spectra of biphenyl were collected at low temperatures to detect the internal librational properties. • Vibrational modes at high frequencies were used to identify the incommensurate structure transition in biphenyl. • Our work provides groundwork for understanding the structural transformation in biphenyl. [ABSTRACT FROM AUTHOR]